Analog to digital converter for well logs

ABSTRACT

This is an analog to digital converter for use with analog data represented by an opaque curve on a translucent record medium. Means are provided to drive the record medium over an enclosure plate having three slits therein. A rotating disc rotates underneath this plate. Radial slits in this disc let light pass through the various slits in the steel plate when coincidence occurs onto a group of photoelectric cells. The light passage is changed by a base line and the opaque curve; such changes are used to obtain a digital representation of the curve at that point.

United States Patent Lindley et al.

n51 3,671,96 1 [451 June 20, 1972 [54] ANALOG TO DIGITAL CONVERTER FORWELL LOGS [72] inventors: Ralph H. Lindley; Richard E. Bickham,

both of Tulsa, Okla.

[73] Assignees: Pan American Petroleum Corporation,

Tulsa, Okla.; Petroleum lnlormation Corporation, Denver, Colo. partinterest to each [22] Filed: April 28, I969 [21] Appl.No.: 819,872

[52] US. Cl. ..340/347 AD, 340/] 74.1 A, 340/347 P [5 1] Int. Cl. "03k13/02 [58] Field of Search ..340/347 A-347 D,

340/ l 74. l A

[56] References Cited UNITED STATES PATENTS 3,052,800 9/1962 Miller..250/2 19 ENCODER 3,165,730 1/1965 Robinson ..340/347 PrimaryExaminer-Maynard R. Wilbur Assistant Etaminer-Robert F. GnuseAnomey-Paul F. Hawley and John D. Gassett [57] ABSTRACT This is ananalog to digital converter for use with analog data represented by anopaque curve on a translucent record medium. Means are provided to drivethe record medium over an enclosure plate having three slits therein. Arotating disc rotates underneath this plate. Radial slits in this disclet light pass through the various slits in the steel plate whencoincidence occurs onto a group of photoelectric cells. The lightpassage is changed by a baseline and the opaque curve; such changes areused to obtain a digital representation of the curve at that point.

3 Claims, 4 Drawing Figures COUNTER 74 RECORD 84 PATENTEDJUH 20 I972SHEET 1 BF 2 omoomm mmhzsou m mmooozm mm Mm N INVENTOR. RALPH H. LINDLEYBY RICHARD E. BICKHM ATTORNEY PATENTEDJUH 2 0 I972 SHEET 2 OF 2 FIG. 4

INVENTOR. RALPH H. LINDLEY BY RICHARD E. BICKHAM ATTORNEY ANALOG TODIGITAL CONVERTER FOR WELL LOGS BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to an analog to digital converterand more particularly to an apparatus for converting analog datarecorded as an amplitude varying curve such as the well known oil fieldwell log into digital values representative of the analog data.

2. Setting of the Invention Over the years in the oil and gas industrythere have been literally hundreds of thousands of well logs run inboreholes drilled in the earth throughout the world. There are manyvarious type logs, such as the resistivity log, gamma ray, velocity log,etc. Normally to obtain each of such logs, an instrument is runvertically through a well bore to measure a selected parameter. Themagnitude of the measured parameter is commonly record-d as a visualcontinuous curve varying with depth on a long, narrow strip of paper,the length of the strip of paper representing the depth axis of the log.In other words, the data is recorded on the paper in analog form. As isknown in the art, it is becoming increasingly desirable to convertanalog data, including these well logs, into digital data having finitevalues which can be used in digital computers.

SUMMARY OF THE INVENTION This concerns an analog to digital converterfor use with analog data represented on a translucent record medium having an opaque curve thereon. There is provided a rotating disc havingslots located on lines radiating outwardly from the center of such disc.A cover plate means is provided adjacent one side of the disc and hasthree slits therein near its outer periphery. Two of the slits (called afirst slit and a third slit) are on lines radiating outwardly from thecenter of the cover plate which is on a line through the center of thedisc and perpendicular thereto. A second slit is on a line perpendicularto a line radiating from the center of said plate. Means are provided tomove the record medium over these three slits. Above the record mediumthere is provided a light source. Photoelectric cells are provided beloweach of the three slits on the side of the rotating disc opposite thelight source. Coincidence of the radial slit of the rotating disc with afirst slit signals a counter to turn on. Coincidence of the radial slitof the disc with the second slit of the plate permits a spot of light topass therethrough. When this spot is interrupted by the opaque curve, anoff signal is generated. The interval between the on and off is thedigital representation of the analog signal at the point being scanned.

Various objects and a better understanding of the invention can be hadfrom the following description taken in conjunction with the drawings.

DRAWINGS FIG. 1 is a schematic drawing of the major components of theanalog to digital converter;

FIG. 2 illustrates a top view of the disc;

FIG. 3 illustrates a top view of the cover plate showing the slitstherein, and

FIG. 4 illustrates a portion of an analog curve which is to be convertedto digital data.

DESCRIPTION OF THE PREFERRED EMBODIMENT Attention is first directed toFIG. 1 of the drawings. Shown thereon is a disc means 10 mounted belowcover plate 12. Disc 10 is supported and rotated by a shaft 14. Shaft 14and plate 12 are both supported from framework 16. An end hearing 15supports the shaft from shelf 17. As shown in FIG. 3, plate 12 has aplurality of slots therein, there being a first slot 18, a second slot20 and a third slot 22. As shown in FIG. 2, disc 10 has a plurality ofslots 24. Slots 24 are on a radial line such as indicated by dotted line26 from the center of the disc 10. The disc 10 is typically about 4 feetin diameter. The slits 24 are typically about 2 inches long and about0.005 inch wide and, of course, extend through the disc. The outer endsof slits 24 are within a few inches of the periphery of disc 10. Theslits 18, 20 and 22 of upper plate 12 are positioned to be adjacent theslots 24 of disc 1.0 as disc 10 is rotated. Slot 18 and slot 22 are onradial lines extending from the center of plate 12. The center of plate12 for this purpose will be deemed to be adjacent the center of disc 10.Slots l8 and 22 are typically about one-half to about three-fourths inchlong and about 0.005 inch wide. Slot 20 is typically about 6 inches longand about 0.005 inch wide. Slot 20 is on a line essentiallyperpendicular to a radial line extending from the center of slot 20 tothe plate 12. Slot 18, if extended, would intercept the end of slit 20.Slit 22, if extended, would be just to the right of the end of slit 20.The relationship of these slots to the record will be discussedhereinafter.

Mounted on top of plate 12 is means for driving the record medium 30containing the analog to be converted across the slots 18, 20 and 22 ofFIG. 3. This includes a chart or record medium 30, a storage roll 32, apaper drive means 35 and paper take-up 34. These charts are preferablymade of paper having perforating along the edges so that positive drivesprockets can drive these curves.

We shall now discuss the power mechanism for driving the rotating disc,the paper drive sprockets and the pulse generator. This includes a basicmotor 38 whose output is mechanically coupled by a drive chain 40 topulley 42 which is fixed to shaft 14 of the rotating disc 10. Motor 38is supported from shelf 17. Shaft 14 is mechanically coupled to a pulsegenerator 44 and paper drive sprockets 35. Pulse generator 44 isconveniently a commercially available encoder which has as an output aseries of pulses, the rate of such pulses being directly proportional tothe rate of rotation of shaft 14 as the shaft of encoder 44 ismechanically coupled to shaft 14. Shaft 14 is also mechanicallyconnected to drive sprockets 35 so that the paper record medium isdriven at a rate directly proportional to the rate of rotation of shaft14. This portion of the drive mechanism can include drive chain 37 andgear 39 driven by power taken by direct mechanical coupling from shaft[4. Endless chain 37 is also guided by sheaves 41 and 43 which aresupported from frame 16. It is thus seen that the rotation of disc 10,the rate of movement of record medium 30 and the rate of generation ofpulses from encoder 44 are all synchronized or proportional. Thus, ifthe rate of rotation of disc 10 fluctuates, it does not change theaccuracy of the digitizing.

Attention is now briefly turned to FIG. 4. Shown thereon is a recordmedium 30 upon which is placed the curve 52. The record medium isprovided with a series of sprocket holes 57. All of the record medium 30is translucent except for line or curve 52 and margin 56, which areopaque. Shown on there is a base line 54 which is defined by the edge ofthe dark margin 56 or, stated differently, the boundary between theopaque margin and the translucent portion of the record medium. Thedirection of scan is indicated by arrow 58. For scan 58 it is desired toobtain a measure of the interval 60 which is the interval or distancebetween the base line 54 and the curve 52. This is a measure of theamplitude at this point.

Attention is now directed back to FIG. 1 which shows that portion of themechanism which is directly concerned with obtaining the measure of theinterval 60. There is a light source 62 directly above the record medium30. Directly under the enclosure of disc 10 are three photoelectriccells. There is one under each of the slits 18, 20 and 22 of FIG. 3.These are photocells 64, 66 and 68 which are respectively under slots20, 18 and 22. The horizontal position of these photocells is relativeto the slits as indicated by dotted circles in FIG. 3. As slot 20 israther long, a lens means 70 is provided between photocell 64 and slot20 to focus any light which passes through the slot onto the surface ofphotocell 64.

It will be recalled that encoder 44 has a continuous output of signalsdirectly proportional to the rate of rotation of shaft 14. It is desiredto count those pulses which occur during the rotation of slit 24 betweenbase line 54 and curve 52. Thus, we obtain a measure of that intervalsuch as interval 60 of base line 54. We therefore start counting whenbase line 54 is reached and stop counting when curve 52 is reached bythe scanning mechanism. We will discuss ways by which that isobtained.'The output pulses from encoder 44 are connected to a gate 72.Counter 74 is any commercial counter which can count the pulses fromencoder 44.'Upon a write command, it transmits information showing thenumber of pulses counted and then resets itself to zero. Gate 72 is anyof the well known types which is opened when it has a signal fed theretoon conductor line 76. Conductor line 76 is connected to the output offlip flop 78. Flip flop 78 is turned on and off by signal meansindicating that the scanning means has encountered base line 54 andcurve 52, respectively. Thus, the "on input of flip flop 78 is connectedby a conductor line 80 to photoelectric cell 66 and the off input toflip flop 78'is connected by line 82 to the output of photoelectric cell64. Flip flop 78 is of a type which has a continuous output signal online 76 when it has been turned on by a signal on the on input. Thissignal stays on until the flip flop 78 receives a signal on the "oiTinput, at which time the output of flip flop 78 is stopped. Thus, it isseen that gate 72 has a signal which causes it to be opened during theinterval from the time in which photocell 66 gives off its first signalto the time in which photoelectric cell 64 emits its off signal.

Photoelectric cell 66, as stated above, is directly below slot 18. Thepaper or record medium 50 passes over this slot as well as the othertwo. The base line 54, as shown in FIG. 3, is

directly over slot 18 so that a part of the slot 18 is blanked off 7 bythe dark margin 56 and a part is adjacent the translucent part of therecord. The boundary between margin 56 and the translucent portion isbase or reference line 54. This reference line 54 travels under slot 18.As disc 10 rotates and slot 24 becomes aligned with slot 18, lightpasses therethrough onto photoelectric cell 66. This causes this cell 66to emit a signal which turns flip flop 78 on. This flip flop will stayon until it receives an off signal from photocell 64. As disc 10rotates, it passes along slot 20. This permits a point of light to passthrough that portion of the two slits which are in coincidence.Photocell 64 is of a type which will emit a signal when the light to itis interrupted. This occurs when line or curve 52, as shown in FlG.'4,is encountered. When flip flop 78 receives an off signal, it no longerhas an output signal. Thus, it is seen that gate 72 is open from thetime at which base line 54 was encountered to the encountering of line52. The number of pulses which were emitted during this time isindependent of the time which this scanning consumed. It is dependentonly on the rotation of disc 10. Thus, the number of pulses passed bygate 72 is the direct measure of the interval 60. This output of gate72is transmitted to a counter 74 which counts these puldicating thatanother radial line or slit 24 has again encountered e base line 54. Asthe disc rotates it is seen that the paper or record medium 30 is alsomoved. Thus, each scan is sea. The counter is of a type which when itreceives a write" A pulse will transmit to record 84 an indication ofthe number of pulses counted during the counting interval. The writepulse is obtained from photoelectric cell 68 which emits a signal 7 whenslot 24 of disc 10 is aligned with slot 22 of plate 12.

It is seen that when disc 10 rotates there is a continuous output ofsignals from encoder 44 which is directly proportional to the rotationof the disc. The number of pulses generated between the encountering ofthe base line 54 and the curve 52 by the scanning mechanism is countedand recorded on record 84. A pulse from generator 66 turns the flip flop78 on to permit the counter to start. Photoelectric cell 66 is of thetype which has an output signal only upon the receiving of light. Theflip flop stays on until it receives an ofi signal from photoelectriccell 64 which is of the type which emits a pulse when light to it isinterrupted. It will be noted that light to photoelectric cell 64 willagain be interrupted when the radial for a succeedingly different depthalong the well log. The interval between the digital measurement can bedetermined by the rate of movement of the record medium compared to therotation of the disc. By having a known depth starting point and a knowninterval between each scan, the digital representation for the variousintervals scanned is readily correlated with those depths.

While the above preferred embodiment has been described with a greatdeal of detail, it is possible for various variations therein withoutdeparting from the spirit or scope of the invention.

We claim:

1. An analog to digital converter for use with analog data representedon a record medium having a curve thereon of different opticalcharacteristics from the record medium, there being a base line for anysuch curve, the combination which comprises:

a disc means, said disc means having a plurality of slits near the outerperiphery thereof, said slits being located on lines radiating outwardlyfrom the center of said disc means;

means to rotate said disc means about its center;

a plate means on one side ofsaid disc means and adjacent thereto, saidplate means having a first slit located on a line radiating outwardlyfrom a point on said plate means i which intercepts a line through thecenter of said disc and perpendicular thereto and a second slit near theouter edge of said plate means and which is perpendicular to a linepassing through the said center of said plate means; means to move saidrecord medium across the outer surface I of said plate means across saidslits and in a direction perpendicular to said second slit and at a rateproportional to the rotation of said disc means;

a light source adjacent said slits and arranged to direct light throughsaid record medium toward said slits;

a first photoelectric cell adjacent said first slit on the opposite sideof said disc from said light source to emit an on" signal each time saidslit is in coincidence with any one of said disc slits;

a second photoelectric cell adjacent said second slit to emit an off"signal each time said curve interrupts light directed toward said secondphotoelectric cell;

means to determine a measure of the interval between said on" signal andsaid off signal; and

record means to record such determined measure.

2. An apparatus as defined in claim 1 including a third slit 7 on a lineradiating outwardly from the center of said plate, the radial distancebetween said first slit and said third slit being sufiicient toaccommodate the maximum amplitude of said curve; and

a third photoelectric cell adjacent said third slit and located on theopposite side of said disc from said light source for emitting a writesignal upon light striking said third cell.

3. An apparatus as defined in claim 2 wherein said counter includes afirst temporary storage means for storing the interval measured by saidfirst measuring means, and including means to transfer the datarepresenting the interval stored in said temporary storage means to saidrecord means photoelectric cell.

* I I i

1. An analog to digital converter for use with analog data representedon a record medium having a curve thereon of different opticalcharacteristics from the record medium, there being a base line for anysuch curve, the combination which comprises: a disc means, said discmeans having a plurality of slits near the outer periphery thereof, saidslits being located on lines radiating outwardly from the center of saiddisc means; means to rotate said disc means about its center; a platemeans on one side of said disc means and adjacent thereto, said platemeans having a first slit located on a line radiating outwardly from apoint on said plate means which intercepts a line through the center ofsaid disc and perpendicular thereto and a second slit near the outeredge of said plate means and which is perpendicular to a line passingthrough the said center of said plate means; means to move said recordmedium across the outer surface of said plate means across said slitsand in a direction perpendicular to said second slit and at a rateproportional to the rotation of said disc means; a light source adjacentsaid slits and arranged to direct light through said record mediumtoward said slits; a firSt photoelectric cell adjacent said first sliton the opposite side of said disc from said light source to emit an''''on'''' signal each time said slit is in coincidence with any one ofsaid disc slits; a second photoelectric cell adjacent said second slitto emit an ''''off'''' signal each time said curve interrupts lightdirected toward said second photoelectric cell; means to determine ameasure of the interval between said ''''on'''' signal and said''''off'''' signal; and record means to record such determined measure.2. An apparatus as defined in claim 1 including a third slit on a lineradiating outwardly from the center of said plate, the radial distancebetween said first slit and said third slit being sufficient toaccommodate the maximum amplitude of said curve; and a thirdphotoelectric cell adjacent said third slit and located on the oppositeside of said disc from said light source for emitting a ''''write''''signal upon light striking said third cell.
 3. An apparatus as definedin claim 2 wherein said counter includes a first temporary storage meansfor storing the interval measured by said first measuring means, andincluding means to transfer the data representing the interval stored insaid temporary storage means to said record means upon receiving said''''write'''' signal from said third photoelectric cell.